Radiation-induced meningiomas.

Radiation-induced meningiomas (RIMs) became more common as the use of ionizing radiation was adopted in the treatment of medical conditions, both benign and malignant. Currently, RIMs represent the most common radiation-induced tumors. They are heterogeneous in terms of patient characteristics, radiographic appearance, genetics, pathology, symptoms, and management strategies. They tend to occur in a younger population and are generally more aggressive in nature than their spontaneous counterparts. Their characteristics also vary based on the dose of radiation received, which is most commonly separated into low dose (<10Gy) and high dose (>10Gy). The importance of the dosing classification is that it can provide insight into the nature and biologic behavior of the tumor. Given their heterogeneity, RIMs pose significant challenges in management. While surgical resection remains the preferred treatment when feasible, recent data supports stereotactic radiosurgery (SRS) as a comparable alternative. Although there is more knowledge about the molecular pathways leading to RIMs, targeted drug therapy is still limited and is the focus of current research.

Surgical Cavity Constriction and Local Progression Between Resection and Adjuvant Radiosurgery for Brain Metastases.

Stereotactic radiosurgery (SRS) to a surgical cavity after brain metastasis resection is a promising treatment for improving local control. The optimal timing of adjuvant SRS, however, has yet to be determined. Changes in resection cavity volume and local progression in the interval between surgery and SRS are likely important factors in deciding when to proceed with adjuvant SRS. We conducted a retrospective review of patients with a brain metastasis treated with surgical resection followed by SRS to the resection cavity. Post-operative and pre-radiosurgery magnetic resonance imaging (MRI) was reviewed for evidence of cavity volume changes, amount of edema, and local tumor progression. Resection cavity volume and edema volume were measured using volumetric analysis. We identified 21 consecutive patients with a brain metastasis treated with surgical resection and radiosurgery to the resection cavity. Mean age was 57 yrs. The most common site of metastasis was the frontal lobe (38%), and the most common primary neoplasms were lung adenocarcinoma and melanoma (24% each). The mean postoperative resection cavity volume was 7.8 cm(3) and shrank to a mean of 4.5 cm(3) at the time of repeat imaging for radiosurgical planning (median 41 days after initial post-operative MRI), resulting in a mean reduction in cavity volume of 43%. Patients who underwent pre-SRS imaging within 1 month of their initial post-operative MRI had a mean volume reduction of 13% compared to 61% in those whose pre-SRS imaging was ≥1 month (p=0.0003). Post-resection edema volume was not related to volume reduction (p=0.59). During the interval between MRIs, 52% of patients showed evidence of tumor progression within the resection cavity wall. There was no significant difference in local recurrence if the interval between resection and radiosurgery was <1 month (n=8) versus ≥1 month (n=13, p=0.46). These data suggest that the surgical cavity after brain metastasis resection constricts over time with greater constriction seen in patients whose pre-SRS imaging is ≥1 month after initial post-operative imaging. Given that there was no difference in local recurrence rate, the data suggest there is benefit in waiting in order to treat a smaller resection cavity.

A Dorsal SHH-Dependent Domain in the V-SVZ Produces Large Numbers of Oligodendroglial Lineage Cells in the Postnatal Brain.

Neural stem cells in different locations of the postnatal mouse ventricular-subventricular zone (V-SVZ) generate different subtypes of olfactory bulb (OB) interneurons. High Sonic hedgehog (SHH) signaling in the ventral V-SVZ regulates the production of specific subtypes of neurons destined for the OB. Here we found a transient territory of high SHH signaling in the dorsal V-SVZ beneath the corpus callosum (CC). Using intersectional lineage tracing in neonates to label dorsal radial glial cells (RGCs) expressing the SHH target gene Gli1, we demonstrate that this region produces many CC cells in the oligodendroglial lineage and specific subtypes of neurons in the OB. The number of oligodendroglial cells generated correlated with the levels of SHH signaling. This work identifies a dorsal domain of SHH signaling, which is an important source of oligodendroglial cells for the postnatal mammalian forebrain.

Primary cilia are required in a unique subpopulation of neural progenitors.

The apical domain of embryonic (radial glia) and adult (B1 cells) neural stem cells (NSCs) contains a primary cilium. This organelle has been suggested to function as an antenna for the detection of morphogens or growth factors. In particular, primary cilia are essential for Hedgehog (Hh) signaling, which plays key roles in brain development. Their unique location facing the ventricular lumen suggests that primary cilia in NSCs could play an important role in reception of signals within the cerebrospinal fluid. Surprisingly, ablation of primary cilia using conditional alleles for genes essential for intraflagellar transport [kinesin family member 3A (Kif3a) and intraflagellar transport 88 (Ift88)] and Cre drivers that are activated at early [Nestin; embryonic day 10.5 (E10.5)] and late [human glial fibrillary acidic protein (hGFAP); E13.5] stages of mouse neural development resulted in no apparent developmental defects. Neurogenesis in the ventricular-subventricular zone (V-SVZ) shortly after birth was also largely unaffected, except for a restricted ventral domain previously known to be regulated by Hh signaling. However, Kif3a and Ift88 genetic ablation also disrupts ependymal cilia, resulting in hydrocephalus by postnatal day 4. To directly study the role of B1 cells' primary cilia without the confounding effects of hydrocephalus, we stereotaxically targeted elimination of Kif3a from a subpopulation of radial glia, which resulted in ablation of primary cilia in a subset of B1 cells. Again, this experiment resulted in decreased neurogenesis only in the ventral V-SVZ. Primary cilia ablation led to disruption of Hh signaling in this subdomain. We conclude that primary cilia are required in a specific Hh-regulated subregion of the postnatal V-SVZ.

Cavernous and inferior petrosal sinus sampling and dynamic magnetic resonance imaging in the preoperative evaluation of Cushing's disease.

The surgical management of Cushing's disease is often complicated by difficulties detecting corticotropic adenomas. Various diagnostic modalities are used when conventional magnetic resonance imaging (MRI) is negative or inconclusive. We sought to analyze our use of two such modalities in the surgical management of Cushing's disease: (1) cavernous/inferior petrosal sinus sampling (central venous sampling, CVS) for adrenocorticotropic hormone and (2) dynamic MRI (dMRI). We conducted a single-center, retrospective review of all patients with Cushing's disease treated by a single neurosurgeon with endonasal transsphenoidal surgery. Accuracy of adenoma localization with CVS and dMRI was analyzed. Ninety-one consecutive patients were included. Pathology confirmed an adenoma in 66. Preoperative dMRI and CVS were performed in 40 and 37 patients, respectively, with 20 undergoing both studies. Surgical pathology was positive for adenoma in 31 dMRI patients, 25 CVS patients, and 13 who underwent both. Among patients with pathology confirming an adenoma, dMRI identified a lesion in 96.8% and correctly lateralized the lesion in 89.7%, while CVS correctly lateralized in 52.2-65.2% (depending on location of sampling). Among patients with both studies, dMRI and CVS correctly lateralized in 76.9 and 61.5-69.2%, respectively. Accuracy of CVS improved if only patients with symmetric venous drainage were considered. In this mixed population of Cushing's disease patients, dMRI was more accurate than CVS at localizing adenomas, supporting the use of advance MRI techniques in the work-up of Cushing's disease. CVS, however, remains an important tool in the workup of Cushing's syndrome.

Persistent sonic hedgehog signaling in adult brain determines neural stem cell positional identity.

Neural stem cells (NSCs) persist in the subventricular zone (SVZ) of the adult brain. Location within this germinal region determines the type of neuronal progeny NSCs generate, but the mechanism of adult NSC positional specification remains unknown. We show that sonic hedgehog (Shh) signaling, resulting in high gli1 levels, occurs in the ventral SVZ and is associated with the genesis of specific neuronal progeny. Shh is selectively produced by a small group of ventral forebrain neurons. Ablation of Shh decreases production of ventrally derived neuron types, while ectopic activation of this pathway in dorsal NSCs respecifies their progeny to deep granule interneurons and calbindin-positive periglomerular cells. These results show that Shh is necessary and sufficient for the specification of adult ventral NSCs.

Utility of the immediate postoperative cortisol concentrations in patients with Cushing's disease.

BACKGROUND: Several investigators have recommended serial measurements of serum cortisol in the days following pituitary surgery to identify patients at risk of recurrence. OBJECTIVE: We systematically reviewed the literature on this topic and analyzed the usefulness of this test in our own patient population. METHODS: We identified studies publishing data regarding recurrence rates after transsphenoidal surgery for Cushing's disease, focusing on studies with data regarding patients with early postoperative cortisol levels. We determined a cumulative relative risk of having a subnormal vs normal cortisol level postoperatively using a fixed-effects meta-analysis model. Additionally, we analyzed our own patients with Cushing's disease undergoing transsphenoidal surgery and performed Kaplan-Meier analysis of recurrence-free survival for patients with undetectable, subnormal but detectable, and normal immediate 8 AM serum cortisol levels. RESULTS: Fourteen studies met inclusion criteria. The length of follow-up varied between 32 and 115 months. The cumulative rate of recurrence in the group of patients with subnormal cortisol levels was 9% (95% confidence interval: 6%-12%). The cumulative rate of recurrence in the group with normal cortisol levels was 24% (95% confidence interval: 17%-31%). We analyzed 73 of our own patients and found similar recurrence rates in patients with subnormal vs normal early postoperative cortisol levels (4% vs 22%, chi2 test, P < .05). CONCLUSION: Although a subnormal early postoperative cortisol level is predictive of improved outcome after transsphenoidal surgery for Cushing's disease, it is not analogous with cure, nor is a normal level completely predictive of future failure.